1. Field of the Invention
The present invention relates to production testing of electronic devices, and more particularly to production testing of devices designed to operate on analog or digital signals.
2. State of the Art
One aspect of electronic device manufacturing is that electronic devices are quality-tested during production. Today, electronic testing equipment is available for testing a wide variety of parts for an equally wide variety of performance characteristics. Typically, computer-based testers are programmed to put a device through a series of tests and to then evaluate whether the device meets predefined performance criteria. If a device under test (DUT) does not meet the criteria, the device is typically discarded. Because large numbers of devices must be tested during an average production run, and because consumers demand both high quality and low cost, electronic testing equipment and procedures must be as quick and as inexpensive as possible while providing a high degree of accuracy.
For purely digital electronic devices in which all signals of interest are digital, thorough quality testing can be performed quickly and cost effectively during production using conventional digital testers. Typically, digital testers provide sequences of digital test patterns to a device under test and monitor digital output sequences generated by the device. The digital input and output sequences are then used by the digital tester to calculate various device characteristics. Because digital-to-digital operations can be carried out at high speed using well known technology, purely digital devices can be thoroughly tested during production in a timely and cost-effective manner.
For example, FIG. 1(A) is a diagram of a device-testing arrangement 1100 in which a digital tester 1110 is used to directly test a digital DUT 1120. As shown, a digital control line 1115 is coupled between a control output of the digital tester 1110 and a control input of the DUT 1120. A digital input/output connection 1125 is coupled between a digital input/output port of the digital tester 1110 and a digital input/output port of the digital DUT 1120. Though only a single digital control line 1115 is shown, those skilled in the art will appreciate that a plurality of control lines may actually be provided between the digital tester 1110 and the digital DUT 1120. Those skilled in the art will also appreciate that the digital input/output connection 1125 typically includes a plurality of individual connections (e.g., to provide a plurality of bits in a digital word). In practice, the physical connections between the digital tester 1110 and the digital DUT 1120 can be made by placing the digital DUT 1120 in a customized socket mounted on a test platform of the digital tester 1110. The digital tester 1110 can include a micro-controller programmed to evaluate one or more performance characteristics of the digital DUT 1120.
During testing, the digital tester 1110 provides appropriate control signals (e.g., transistor-transistor logic, or TTL, signals) to the digital DUT 1120 via the digital control line(s) 1115 so that the digital DUT 1120 carries out a particular sequence of operations. At the same time, the digital tester 1110 provides and/or receives digital test patterns via the digital input/output connection 1125. By monitoring digital signals produced by the digital DUT 1120, the digital tester 1110 can assess, given the control signals and any input test patterns provided by the digital tester 1110, one or more performance characteristics of the digital DUT. For example, if the digital DUT 1120 is a digital counter, the digital tester 1110 can provide a recurring clock pulse to the DUT 1120 via the digital control line 1115 and simultaneously monitor the digital counter output via the digital input/output connection 1125 to ensure that each increment in the digital count is produced accurately by the digital DUT 1120.
Digital testers such as that shown in FIG. 1(A) are relatively inexpensive and provide for quick and thorough testing of digital devices during production. For example, the time required for such a digital tester to evaluate all 256 possible bit patterns output by an 8-bit digital counter is sufficiently short that each counter in a production run can be completely tested without significantly slowing down the overall production process. However, this is not the case when the FIG. 1(A) digital tester is used to directly test a mixed-signal device having both analog and digital nodes. This is due, in part, to the relatively slow conversion times associated with parametric measuring units in conventional digital testers. Thus, mixed-signal devices which process both digital and analog signals present a more difficult quality-testing challenge, and the high-speed, cost-effective digital-to-digital testing operations described above are not directly applicable.
As a result, conventional testers trade off speed against cost with respect to quality-testing of mixed-signal devices. For example, conventional digital testers which use parametric measuring units provide analog-to-digital and digital-to-analog conversions as necessary so that mixed-signal devices can be tested in a manner analogous to that of digital devices. However, because the conversion times provided by available digital testers are prohibitively long, these digital-tester systems are typically configured to test only a small subset of the overall functionality of a DUT. As a result, the quality assurance provided by such systems is diminished.
For example, FIG. 1(B) is a block diagram of a device-testing arrangement 1200 in which a digital tester 1210 is used to directly test a mixed-signal device 1220 having a digital input and an analog output, such as a digital-to-analog converter. As shown, digital control line 1215 is coupled between a control output of the digital tester 1210 and a control input of the mixed-signal digital-to-analog DUT 1220. Additionally, a digital input connection 1225 is coupled between a digital output port of the digital tester 1210 and a digital input port of the mixed-signal DUT 1220, and an analog output line 1235 is coupled between an analog output of the mixed-signal DUT 1220 and an analog input of the digital tester 1210. As with FIG. 1(A), those skilled in the art will appreciate that each of the digital control line 1215, the digital input connection 1225 and the analog output line 1235 can include a plurality of lines depending upon the precise device being tested.
In operation, the digital tester 1210 provides appropriate control signals to the mixed-signal DUT 1220 via the digital control line(s) 1215 so that the mixed-signal DUT 1220 carries out a particular sequence of operations. At the same time, the digital tester 1210 can provide a sequence of digital test patterns to the digital input of the mixed-signal DUT 1220 via the digital input connection 1225. By monitoring the analog output of the mixed-signal DUT 1220 (e.g., using a standard internal parametric measuring unit), the digital tester 1210 can assess, given the digital control signals and any input test patterns provided by the digital tester 1210, one or more performance characteristics of the mixed-signal DUT 1220.
For example, if the mixed-signal DUT 1220 is a digital-to-analog converter, the digital tester 1210 can provide the converter with a digital input pattern via the digital input connection 1225 and then instruct the converter, via the digital control line 1215, to perform a conversion. Once the conversion is complete, the digital tester 1210 can convert the resulting analog signal, received via the analog output connection 1235, into a digital signal which can be compared to the known digital input pattern to ensure that the converter under test is functioning properly. This sequence of operations can be repeated with multiple digital input patterns to test the converter at different points within its designed range of operation. However, the level of quality assurance which can be obtained using a system such as that depicted in FIG. 1(B) is less than ideal.
As another example, FIG. 1(C) is a block diagram of a device-testing arrangement 1300 in which a digital tester 1310 is used to directly test a mixed-signal device 1320 having an analog input and a digital output, such as an analog-to-digital converter. As shown, a digital control line 1315 is coupled between a control output of the digital tester 1310 and a control input of the analog-to-digital DUT 1320. Additionally, an analog input line 1325 is coupled between an analog output of the digital tester 1310 and an analog input of the mixed-signal DUT 1320, and a digital output connection 1335 is coupled between a digital output port of the mixed-signal DUT 1320 and a digital input port of the digital tester 1310. Again, those skilled in the art will appreciate that each of the digital control line 1315, the analog input line 1325 and the digital output connection 1335 can include a plurality of lines depending upon the precise mixed-signal device being tested.
In operation, the digital tester 1310 provides appropriate control signals to the mixed-signal DUT 1320 via the digital control line(s) 1315 so that the mixed-signal DUT 1320 carries out a particular sequence of operations. At the same time, the digital tester 1310 can provide an analog test signal (e.g., using a parametric measuring unit) to the analog input of the mixed-signal DUT 1320 via the analog input line 1325. By monitoring the digital output of the mixed-signal DUT 1320 via the digital output connection 1335, the digital tester 1310 can assess, given the control signals and any input test signals provided by the digital tester 1310, one or more performance characteristics of the mixed-signal DUT 1320.
For example, if the mixed-signal DUT 1320 is an analog-to-digital converter, the digital tester 1310 can provide the converter with an analog test signal via the analog input line 1325 and then instruct the converter, via the digital control line 1315, to perform a conversion. Once the conversion is complete, the digital tester 1310 can read the resulting digital signal via the digital output connection 1335 and compare it with the digital pattern known to correspond to the analog test signal. This sequence of operations can be repeated with various analog input levels to test the converter at different points within its designed range of operation. However, like the system of FIG. 1(B), the level of quality assurance which can be obtained using a system such as that depicted in FIG. 1(C) is less than ideal.
In summary, the digital tester of FIG. 1(A) is inappropriate for use with mixed-signal devices and, because the digital testers 1210, 1310 of FIGS. 1(B) and 1(C) are not designed for use with analog signals, the time required to test a full range of digital patterns is impractical. As a result, conventional digital-tester systems have been configured as reduced function testers for testing a limited number of test patterns, thereby speeding up the overall testing process while sacrificing quality assurance.
The sacrifice in quality assurance associated with these reduced-function testers can be significant. For example, a converter is ideally tested over its full range of operation to obtain a transfer characteristic, or transfer curve, for the converter. Given the transfer curve, meaningful parameters such as the integral linearity error (ILE) and the differential linearity error (DLE) of the converter can be computed and compared to predefined levels of acceptability. Previous attempts to avoid this sacrifice in quality assurance have resulted in the development of expensive, customized, high-speed mixed-signal device testers.
For example, FIG. 1(D) is a block diagram of a customized device-testing arrangement 1400 in which a mixed-signal tester 1410 is used to directly test a mixed-signal device 1420 operating on both analog and digital signals. As shown, a digital control line 1415 is coupled between a control output of the mixed-signal tester 1410 and a control input of the mixed-signal DUT 1420. Additionally, a digital input/output connection 1425 is coupled between a digital port of the mixed-signal tester 1410 and a digital port of the mixed-signal DUT 1420, and an analog input/output line 1435 is coupled between an analog port of the mixed-signal tester 1410 and an analog port of the mixed-signal DUT 1420. Those skilled in the art will appreciate that each of the digital control line 1415, the digital input/output connection 1425 and the analog input/output line 1435 can actually include a plurality of lines depending upon the precise mixed-signal device being tested.
In operation, the mixed-signal tester 1410 provides appropriate control signals to the mixed-signal DUT 1420 via the digital control line(s) 1415 so that the mixed-signal DUT 1420 carries out a particular sequence of operations. At the same time, the mixed-signal tester 1410 can provide analog and/or digital input test signals to the mixed-signal DUT 1320 via the analog input/output line 1425 and the digital input/output connection 1425. By monitoring the analog and/or digital output of the mixed-signal DUT 1420 (again via the analog input/output line 1425 and the digital input/output connection as appropriate), the mixed-signal tester 1410 can assess, given the control signals and any input test signals provided by the mixed-signal tester 1410, one or more performance characteristics of the mixed-signal DUT 1420.
For example, if the mixed-signal DUT 1420 is an analog-to-digital or digital-to-analog converter, the mixed-signal tester 1410 can provide the converter with an analog or digital input test signal as appropriate, and then instruct the converter via the digital control line 1415 to perform a conversion. Once the conversion is complete, the mixed-signal tester 1410 can receive the resulting analog or digital signal and process it (e.g., using dedicated circuitry within the mixed-signal tester 1410) to ensure that the mixed-signal DUT 1420 is functioning properly.
Because the mixed-signal tester 1410 is specifically configured to work with both analog and digital signals at high speeds, a converter under test can be evaluated over its full range of operation. However, mixed-signal testers such as that depicted in FIG. 1(D) are prohibitively expensive. As a result, quality testing using a system such as that shown in FIG. 1(D) may not be cost effective.
Thus, there is a need for improved methods and apparatus for testing mixed-signal devices in which the functionality of a device under test can be thoroughly tested, both quickly and cost-effectively.